In this paper, we exploit random variation of daily temperature in the United States at both state and county level, from March 1st to October 31st 2020, to study if temperature has a significant effect on COVID19 incidence rate. We find that warmer than average days lead to a lower incidence rate, seven days later. A week in which temperature is consistently one standard deviation above the monthly average in all US states causes 17,754 fewer cases at national level, seven days later. Other weather variables do not have a significant and robust effect on the incidence rate. The effect of temperature is heterogeneous over space and time.